Magnetic disk device having a low-profile motor without deterioration in the strength of the enclosure

ABSTRACT

A magnetic disk drive includes a base constituting at least a face included in an enclosure; a shaft secured to the base; a rotor which rotates around the shaft as a rotary axis; a stator for rotating the rotor; and a magnetic disk secured to the rotor; wherein the stator is disposed on a face facing the base. This improves durability of the magnetic disk drive.

TECHNICAL FIELD

The present invention relates to a magnetic disk drive.

BACKGROUND ART

In recent years there has been a demand for magnetic disk drives with anincreased capacity and a reduced size. Magnetic disk drives having aflat-external dimension of 1.0 inch are brought to the commercial stagein the level of current products.

The conventional magnetic disk drives have an in-hub motor configurationor under-hub motor configuration. The in-hub motor is configured suchthat a magnetic circuit including a rotor and a stator is disposedinside the center hub of a spindle on which disks are stacked, which isnow in most widespread use. The under-hub motor is configured such thata magnetic circuit including a rotor and a stator is disposed nearer abase than a hub portion on which disks are stacked.

The configuration described in Japanese Patent Laid-open No. 6-68592 isan example of disk drive configurations using the in-hub motor.

As shown in FIG. 2 of the above publication, this configuration employsa shaft-fixed type in-hub motor, in which a hub is disposed on a shaftsecured to a base by way of bearings, magnets constituting a rotor aredisposed inside the hub, and a stator is disposed on the base.

It is Japanese Patent Laid-open No. 7-182771 that discloses a magneticdisk drive configuration using the under-hub motor.

As shown in FIG. 2 of this publication, this configuration employs ashaft-fixed type under-hub motor, in which a hub is disposed on a fixedshaft secured to a base by way of bearings, magnets constituting a rotorare disposed below the hub, and a stator is disposed on the base.

There has been an increase in demand for a low-profile magnetic diskdrive in recent years. Although the overall drive can be thinned inprinciple by making individual components thin, these components includeones impossible to make thin simply. One of them is an enclosure.

Since a shaft is a central axis around which a hub rotates irrespectiveof a shaft-rotary type or the shaft-fixed type, a portion of a basepositioned near the shaft needs a certain thickness so as to withstand alarge force exerted on the shaft. In addition, the base needs mass thatovercomes a force due to the rotation of the hub.

Therefore, it is preferable for a characteristic of a recess provided onthe base that the recess be provided at a position away from the shaft.In addition, preferably as the recess is provided at a position nearerthe shaft, the area of the recess should be made smaller.

However, since the stator is formed so as to cover the shaft in theabove prior art, if it is intended to make a low-profile device bylowering the position of the stator to the base side, it is inevitableto form the recess circularly or annularly in the base around the shaft.That is, the prior art has not taken into consideration that theenclosure is made thinner with care taken to the durability thereof.

In addition, the prior art simple describes that the stator is mountedon the base; no consideration is given to the arrangement among thestator and other members, more specifically, the relation between thestator and the enclosure facing the base; furthermore, a change in thestrength of the enclosure itself is not taken into consideration.

That is, an object of the present invention is to make a magnetic diskdrive thinner with the durability of an enclosure improved.

Besides the enclosure, components impossible to make smaller include aspindle motor and a battery.

For a magnetic disk, it is necessary to retract a magnetic head from thesurface of the magnetic disk, where the magnetic head is placed, beforerotation of the spindle motor is stopped. When this is carried out in anormal operation, an external power source is used for it; however, inthe event of unplanned power interruption, the external power sourcecannot be used.

In order to perform such operation, an internal power source connectedto a motor (VCM) for shifting the magnetic head is needed, and ingeneral a battery performs the function. A large-scaled battery with alarge capacity is inevitably selected because of a battery capacitynecessary for the battery.

If small batteries are dispersedly mounted on a board, this posesproblems that performance is degraded due to wiring resistance, amounting area is increased, and so forth. Concrete measures to solve theproblems are not taken into consideration.

Accordingly, another object of this invention is to prevent adeterioration in the durability of an enclosure as well as to reduce abattery mounting area, and to downsize a magnetic disk drive as well asto thin the drive down.

DISCLOSURE OF INVENTION

According to one aspect of the present invention to achieve the aboveobjects, there are provided a base constituting at least a face includedin an enclosure; a shaft secured to the base; a rotor which rotatesaround the shaft as a rotary axis; a stator that rotates the rotor; anda magnetic disk, the stator being disposed on a face facing the base.Since the stator is disposed not on the base but on the face facing thebase in this aspect, a portion of an area far from the shaft may bereduced, whereby a thickness required for a portion of the base in thevicinity of the shaft can be secured. In other words, the employment ofthe configuration of this aspect can make a magnetic disk drive thinwhile suppressing a deterioration in durability of the enclosure.

According to another aspect of the prevent invention, there are provideda soft magnetic metal plate, wiring disposed on opposite surfaces of thesoft magnetic metal plate, and a through hole bringing the wiringdisposed on the opposite surfaces of the soft magnetic metal plate intoconduction, and the wiring and the through hole are spirally configuredto form a coil. With this configuration, since the board manufacturingprocess can be used as it is, a stator can be made thin. Since themanufacturing process of electronic circuit boards (a printed boardmanufacturing technique) is employed, an electronic board and a statorcore can be formed from the same material. In addition, if they are madefrom the same material, they are made by one operation, whereby amagnetic disk drive can be made thin while suppressing a deteriorationin durability of an enclosure.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a top view of a magnetic disk drive;

FIG. 2 is a sectional view of FIG. 1, taken along line A1–A2;

FIG. 3 is a sectional view of FIG. 1, taken along line B1–B2.

FIG. 4 is an enlarged view of an area C in FIG. 1;

FIG. 5 is a sectional view of FIG. 4, taken along line D1–D2;

FIG. 6 is a sectional view of FIG. 4, taken along line E1–E2;

FIG. 7 is a sectional view of an electronic circuit forming portion of ametal core wiring board; and

FIG. 8 is a table indicative of stator thicknesses and motorperformances.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a description will be made of a configuration of a magneticdisk drive according to the present invention with reference to thedrawings.

The magnetic disk drive principally includes a magnetic head positioningmechanism, a magnetic disk, an enclosure (a cover and a base) made ofaluminum, a connector, a stator, a rotor portion, and a stator portion.The device has the same outer dimensions (43 mm×36 mm×3.3 mm) as acompact flush memory type 1 does.

FIG. 1 is a top view of the magnetic disk drive with a cover placed atthe upper surface of the enclosure of the drive removed. Incidentally,in an actual magnetic disk drive, a board including a stator is bondedto an upper cover with adhesive before the board is fixedly screwed tothe upper cover.

In FIG. 1, reference numeral 100 denotes a metal core wiring board 100including a soft magnetic metal plate as a core material. The metal corewiring board 100 is provided with two holes in general. These two holesare provided for the magnetic head positioning mechanism 110 and amagnetic disk rotation central shaft 120, respectively. The magnetichead positioning mechanism 110 includes an arm 111 on which a magnetichead is mounted. A rotor magnet (permanent magnet) 121 and a magneticdisk 122 disposed below the wiring board are disposed in the hole 120. Astator coil 101 and wiring are formed in areas other than the holes ofthe metal core wiring board 100. Incidentally, numeral reference 102denotes a screw hole for securing the metal core wiring board to theenclosure 103.

Part of the configuration of the magnetic disk drive according to theinvention will be described with reference to FIG. 2 showing a sectionalportion taken along line A1–A2 in FIG. 1. The magnetic head positioningmechanism 110 is rotatably mounted to a fixed shaft 112 by way of abearing 113. The magnetic head positioning mechanism 110 is providedwith a coil assembly 114 of a voice coil motor (VCM) for positioning themagnetic head 117 and a head arm assembly 111 on which the magnetic head117 is mounted. The coil assembly 114 is disposed between a magnet 115and a yoke 116. The VCM of the magnetic head positioning mechanism iscomposed of the members 110 to 116. An inside mechanism protection cover104 of the magnetic disk drive is provided on a side facing theenclosure 103.

Part of the configuration of the magnetic disk drive according to theinvention will then be described with reference to FIG. 3 showing asection taken along line B1–B2 in FIG. 1. The rotor magnet 121 and themagnetic disk 122 are mounted to the magnetic disk rotation centralshaft 120, which is a center around which the magnetic disk turns. Themagnetic disk rotation central shaft 120 is mounted to the bearing 124by way of a movable rotary shaft 123. The bearing is secured to theenclosure 103. A hub is a generic name for the members 120, 121, 123 and124 that transmit rotation to the magnetic disk.

A connector 105 having a plurality of signal pins formed thereon isdisposed at an end of the metal core wiring board 100 to send or receivean electrical signal to or from the outside. A sealing resin is appliedto the inside of a housing of the connector and then cured with heat soas to seal through holes formed in the connector. This is to preventdust entering from the outside from sticking to the surface of themagnetic disk. A magnetic shield thin plate 106 is mounted on the metalcore wiring board.

The stator is bonded to the inside of the cover overlapping the magneticdisk; the inside of the cover is positioned in a centrifugal direction,relative to the annular permanent magnet, of the shaft around which therotor turns.

As shown in FIGS. 2 and 3, since the metal core wiring board 100 inwhich the core is made by stacking soft magnetic metal plates is bondedto the cover that is the upper portion of the enclosure, the metal corewiring board 100 substantially constitutes the upper surface member ofthe enclosure. Therefore, the upper surface of the enclosure is enhancedin strength; the overall magnetic disk drive is improved inimpact-resistance and can be made thinner.

In addition, since the metal core wiring board is used as the core ofthe stator, which is stronger in shock than other members, the thinsmall-sized magnetic disk drive is realized while the overall drive isimproved in durability to shock.

The connector having the plurality of signal pins formed thereon isdisposed at the end of the cover to send or receive an electrical signalto or from the outside. The sealing resin is applied to the inside ofthe housing of the connector and then cured with heat so as to preventdust entering from the outside from sticking to the surface of themagnetic disk, thereby sealing the through holes for physical electricalconnection with formed terminal pins.

A description will then be made of the relation between the stator andthe rotor magnet with reference to FIG. 4 which is an enlarged view ofan area C in FIG. 1.

Tip portions 107 of stator poles (core pieces) are disposed via radialgaps outside the annular rotor magnet (permanent magnet) 121, which isdivided, and magnetized, into 16 poles in a circumferential direction;the rotor magnet 121 is provided at the generally outer end of therotor. Stator poles 108 have 24 poles which are 1.5 times the number ofpoles of the annular permanent magnet. The rotor is rotated by amagnetic force produced between the tip portions 107 of the stator polesand the rotor magnet 121.

The stator has as a core a stack of the soft magnetic metal plates madeof silicon iron. Coils in which wires and through holes are connected toeach other in a winding manner are disposed around the stator poles 108by way of insulating films. An electric current supplied to the statorcoil is controlled so as to control a magnetic field fed to the rotormagnet, which produces torque rotating the rotor portion. FIG. 4 showsthe coils formed by means of a method for manufacturing a wiring board.The stator poles 108 made of silicon iron core are insulated by anorganic insulating material, and a thin metal plate made of copper isetched on the organic insulating material, whereby wiring is formed likea large number of strips. The wiring layer 132 is part of the statorcoil.

The coil for stator pole will be described with reference to FIG. 5which is a sectional view taken along line D1–D2 in FIG. 4. In thisembodiment, there are provided four layers of the stator cores, and fourwiring layers, that is, two wiring layers each placed above and underthe stator core layer. The stator pole is covered in the circumferencethereof with an organic insulating material 131. Through holes are boredin portions of the organic insulating material so as to extend throughfrom the front to back thereof, and then the inside of the through holesare subjected to conductive processing with plating, thereby formingtwo-side conductive wiring 133. This wiring is connected to the four,front and back wiring layers 132, 134 so as to form double spirals, andthen this connection is continued in the direction of the central axisE1–E2 of the stator pole in FIG. 4, thereby forming the stator coil. Ifthe wiring layer is one pair of the front and back, a single spiral isformed.

A configuration of the stator pole will be described in detail withreference to FIG. 6 which is a sectional view taken along E1–E2 in FIG.4. The stator pole includes a coil forming portion and the tip portions107 of the stator pole in which no coil is formed. The tip portion ofstator pole 107 which is the core portion of the stator pole has threebonding insulating layers 109 and four layers of stator poles made ofsoft magnetic metal plates, which are alternately stacked to form sevenlayers of cores in total. To form a double wound coil, the coil formingportion includes the wiring layers 132, 134 disposed on the front andback of the soft magnetic plate core layer of the stator pole and fourcoil layers, using the bonding insulating material 131, formed for eachof the front and back. The end face, on the rotor permanent magnet 121side, of the tip portion of the stator pole 107 is covered with theorganic insulating layer 109 to protect the silicon core material.

A minimum value of thickness of the stator is determined by an electriccurrent value that a spindle motor needs to rotate a rotating body at acertain number of rotation; the rotating body in which the magnetic headis disposed via the air gap includes the rotor and the magnetic disk.

In the spindle motor, the stator has 24 poles, and four layers ofsilicon iron each having a thickness of 0.1 mm; the metal wiring layerof the coil portion is 40 μm in thickness; the stator is 0.7 mm inthickness with the insulator layer being 35 μm in thickness; the statorcoil is 150 μm in line width and 100 μm in line interval; and thethrough hole portion has 40 turns in the number of winding per pole with100 μm in outside diameter and 60 μm in inside diameter. Meanwhile, whenthe torque constant of the motor was determined with the rotor magnetbeing 16 poles, 13.2 mm in outside diameter, and 0.7 mm in thickness, itwas about 0.0018 Nm (Newton meter) per 1 A in electric current. Thestator coil was about 6 Ω in DC resistance. The spindle motor was about0.00011 Nm in steady-rotation torque. Accordingly, the spindle motoroperates at about 60 mA in steady current.

Torque constant (Kt) of a motor is generally represented by thefollowing expression;Kt=A×Wb×N×Ns  (1)where A is constant, Wb is a magnetic flux density between a rotor and astator, N is the number of winding coils per pole of the stator, and Nsis the number of poles per phase of the motor.

Assuming that the thickness of the stator portion is the same as that,in an axial direction, of the rotor magnet on the basis of the presentembodiment, and the wiring rule of the stator coil is constant, whenmotor characteristics are calculated with the thickness of the statorchanged, numerical values as shown in FIG. 8 can be obtained.

Taking a stator 0.35 mm thick as an example, when an actual wiring boardis taken into consideration, a single-sided one layer is insufficientfor the wiring layer; therefore, it is necessary to considersingle-sided two wiring layers. The following will be considered asmeasures to be taken: a first case is that the thicknesses of the coiland insulator layer are halved to keep the total thickness thereof to0.35 mm; and a second case is that only the core is made 0.2 mm thickand four wiring layers are used as they are and thereby the totalthickness thereof is made 0.5 mm.

In this consideration, the two cases are different from each other inonly their respective DC resistances of the stator coils; the first caseis 12 Ω while the second case is 6 Ω. The saturated magnetic fluxdensity of the stator pole (1.5 T) leads a saturated current into about0.62 A. The electric current in the steady rotation is 60 mA within therange in which the stator pole is not saturated, which is equivalent tothe example of 0.7 mm thick. In addition, the maximum torque is about60%, which can still be used for a spindle motor. It will be understoodthat the present embodiment can configure a low-profile motor which hasa stator including a metal core wiring board of a thickness greater than0.35 mm.

On the other hand, a limit of greater side thickness of the statordepends on a technique of forming the conductive wiring which uses thefront/back through hole for the coil forming the stator pole. In theconsideration of the technique according to the embodiment, throughholes of 0.11 (aspect ratio 10) were bored in a stator stack core 1.1 mmthick and conductive plating was applied to the inside walls of thethrough holes, which caused variations in plating-thickness. This has aneffect on variations in DC resistance of the coil, which has an effecton characteristics and manufacturing yields. If it is possible to applystable plating to the inside of the through holes with a larger aspect,also a stator core having a thickness of 1.1 mm or more may be used.Thus, it will be understood that according to the manufacturingtechnique of this embodiment the stator which measures 1.4 mm inthickness, that is, the stator core 1.1 mm in thickness and the wiringlayers 0.3 mm in thickness, gives an upper limit thickness of alow-profile motor which uses the metal core wiring board.

The present embodiment has configured a magnetic disk drive which hasthe outer dimensions of 42.8 mm wide by 36.4 mm deep by 3.3 mm thickwith the use of two sets of magnetic head arm assemblies each 0.85 mmthick, a magnetic disk 0.4 mm thick, and a metal core board 0.7 mmthick. If one set of magnetic head arm assembly is used and thethickness of the metal core board is selected on the basis of motorcharacteristics, a magnetic disk drive having a thickness in the rangeof 2.5 mm to 4.0 mm can be realized.

In particular, if one set of magnetic head assembly and a magnetic diskof about 0.7 inch in diameter are employed, a magnetic disk drive havingthe outer dimensions of 21.5 mm wide by 50.0 mm deep by 2.8 mm thick canbe realized.

A description will then be made of a power supply layer with lowimpedance and low DC resistance referring to FIG. 7. This figure is asectional view of an electronic circuit forming portion of the metalcore wiring board. Via holes 142 for through holes in a stator portionand an electronic board portion are formed in two of the stator poles108 made of soft magnetic metal plates, and thereafter, copper-plating141 is applied to the surface thereof. Taking the thickness of aninsulating material consideration so that a distance between the twosoft magnetic metal plates is made 5 to 30 μm after formation of themetal core wiring board, an insulating-bonding layer 109 is interposedbetween the two plates to form a stacked plate. If a silicon steel plateis used as the soft magnetic metal plate, its volume electric resistanceis about 10 μΩcm. A cupper plating film of about 5 μm thickness isformed on the soft magnetic metal plate, cupper being about 1.7 μΩcm involume electric resistance. The soft magnetic metal plate and the cupperplating film are used for an entire ground layer and the power supplylayer, which provides low impedance in a high frequency regionsusceptible to the skin effect.

Semiconductor devices and the like are connected to the power supplylayer or the ground layer by forming a through hole 144 at a positionnear a pad of a power supply system or power supply terminals of thesemiconductor devices 143, and thereby the connection with low impedanceand low DC resistance become possible. In the case of using such a powersupply layer, the wiring board has, even at any portion of 20 mminterval, a DC resistance of several milliohms and an impedance ofseveral hundreds pH or less, which depends on the density of the throughholes. A battery 145 with low inductance and small capacity and abattery 146 with large capacity such as an electrolytic capacitor aremounted on a board at appropriate spaces and connected to the powersupply layer and the ground layer in parallel. This makes it possible toform a power supply system with low impedance over a wide bandwidth fromdirect current to several hundreds megaherzes.

Accordingly, the formation of the low impedance power supply systemincreases flexibility of arrangement of a bypass capacitor or a batteryfor smoothing power supply, which can reduces the area of the board,thereby achieving miniaturization of the overall magnetic disk drive.

Incidentally, a through-connection portion 147 that extends through andconnects the front and back of the metal core wiring board is formed inthe electric circuit forming portion, which attains high density ofwiring. An electronic component 148 is mounted on and electricallyconnected to the wiring board 100 by means of solder 149 or a connectingmethod using metal wires not shown in the figure.

The through hole portions 147 are formed by forming holes in all thesoft magnetic metal plate core layers, filling the holes with aninsulating material before forming holes that extends through the frontand back of the core layer, and forming wiring materials on the insideof the holes with plating to come into conduction. This forming methodis the same method as in the coil formation of the stator pole and theelectronic circuit forming portion. Thus, since the electronic boardportion uses the same layer structure as the stator portion does, bothof them are formed as the same board. In the case of making theelectronic board portion and the stator portion in the same board, ifthe thickness of the layer is entirely made uniform, the electronicboard portion and the stator portion can simultaneously be fabricated byone manufacturing process.

While silicon iron of about 1.5 T in saturated magnetic flux density isused for the soft magnetic core thin plate material in this embodiment,it may be possible to make the device further thinner by using amorphousmaterial of a larger value in the saturated magnetic flux density.

According to the present invention, it is possible to make a magneticdisk drive thinner without lowering the mechanical strength thereof.

INDUSTRIAL APPLICABILITY

As described above, the present invention is useful to a magnetic diskdrive.

1. A magnetic disk drive in an enclosure comprising: a base constitutingat least a face included in the enclosure; a shaft secured only to thebase; a rotor which rotates about the shaft; a stator for rotating therotor, the stator having an annular shape and being circumferentiallydisposed about a periphery of the rotor and in coplanar relation withthe rotor; a magnetic disk secured to the rotor; and wherein the statoris disposed on a surface of the enclosure opposite the base.
 2. Amagnetic disk drive according to claim 1, wherein part of a coil of thestator is disposed at a position nearer the base than a magnet of therotor.
 3. A magnetic disk drive according to claim 1, wherein themagnetic disk is disposed between the stator and the base.
 4. A magneticdisk drive according to claim 3, wherein part of a magnet of the rotoris disposed at a position nearer the magnetic disk than the stator.
 5. Amagnetic disk drive according to claim 1, further comprising a metalcore board on which an electronic component is mounted, wherein thestator includes a core, and the core of the stator is connected to acore of the metal core board.
 6. A magnetic disk drive according toclaim 5, wherein the core of the stator is integrally formed with thecore of the metal core board.